# Upper Rim-Bridged Calix[4]arenes via Cyclization of meta Alkynyl Intermediates with Diphenyl Diselenide

## TL;DR

This paper explores new chemical reactions in calix[4]arenes, revealing unique bridging products and reaction pathways not seen in non-macrocyclic compounds.

## Contribution

The study demonstrates novel cyclization reactions in calix[4]arenes leading to unexpected bridging products and regioselectivity.

## Key findings

- Alkynylcalixarenes were successfully synthesized using Sonogashira coupling with high yields.
- Electrophilic closure with diphenyl diselenide produced unique bridging products, including a 5-endo-dig cyclization never observed before.
- X-ray analysis confirmed the distinct regioselectivity of cyclization reactions in macrocyclic versus aliphatic compounds.

## Abstract

A Sonogashira coupling of meta-iodocalix[4]arene with various terminal acetylenes confirmed that the meta position of calixarene is well addressable, and that both thermal and microwave protocols led to good yields of alkynylcalixarenes. Alkynes thus obtained were subjected to the ferric chloride and diphenyl diselenide-promoted electrophilic closure. It turns out that the calix[4]arenes give completely different bridging products than those described for the non-macrocyclic starting compounds. This can be demonstrated not only by the isolation of products with a six-membered ring (6-exo-dig), but mainly by the smooth formation of the 5-endo-dig cyclization, which has never been observed in the aliphatic series. An attempt at electrocyclization led to a high yield of the 1,2-diketone (oxidation of the starting alkyne), again in contrast to the reaction described for the acyclic derivatives. The structures of the unexpected products were unequivocally established by X-ray analysis and clearly demonstrate how the preorganized macrocyclic skeleton favors a completely different regioselectivity of cyclization reactions compared to common aliphatic compounds.